From the earliest dawn of history, man must have wondered how
the outside world became apparant to him through his eyes. He
must have pondered what forces cause an observing eye to see an
object. Why did the world look light or dark or nature have such
bright colors? Even though early man could not understand the
concept of the physics of light or that perception occurred in
the brain, he must have understood that the eye was the organ
of vision and without eyes we were blind. Thus, the earliest concerns
of the ancient civilizations of India, Babylon, China and Egypt
were certainly to attempt to restore or improve eye sight when
it was failing even without understanding much else. It was the
Greek philosophers (Hippocrates, Aristotle, Plato) who provided
the first known theories concerning the eye, its function, anatomy
and treatment. Originally the Aristotelean idea was that rays of light eminated from the eyes to illuminate the world around. When it was dark, the air became murky so the rays could not penetrate but a candle could burn off the opacity in the air allowing sight to penetrate. Also strangely enough the Homeric Greeks lacked a word for blue. Homer described the sea as "wine colored".

Eventually, Aristotle proposed that visual sensation passed
from the eye to the heart which was at that time considered
the center of sensation and psychic function. The brain
was thought to be a cooling device (Jung, 1984). This cardiocentric
nature of sensation, continued into the middle ages (as depicted
by the sixteenth century illustration, Fig. 1), despite the
direct experimental evidence of Galen (A.D. 129-200). Galen, a
Greek scientist working within the Roman empire, showed that pressing
on the heart in human subjects did not lead to loss of consciousness
or loss of sensation but severing the spinal cord in animals abolished
sensory responses after brain stimulation.

Figure 1. Aristotelian concept of five senses projecting
to the heart either directly or via the "sensus communis"
in the anterior part of the head (lower panel). The upper panel
shows the four (Galen's and Avicennas's) or five (Albertus Magnus's)
brain compartments (from Jung, 1984).

The ideas of the Greeks from centuries B.C. were perpetuated
and preserved by the writings and drawings of the Arab world until
well into the middle ages A.D.. Thus, one of the earliest diagrams
of the eye was from an ancient Arab manuscript (circa A.D. 860)
and this was probably a copy of an older Greek illustration now
lost (Fig. 2, below) (Polyak, 1957).

Figure 2. The earliest arabic drawing of the structure
of the eye (from Polyak, 1957).

According to early ideas, the eye had a central crystalline
lens which had a photoreceptor role. Furthermore, the belief was
that the optic nerve was hollow and that a mysterious visual
spirit existed in front of the lens (Fig. 2). Interestingly,
the general theory advanced by the majority of Greek anatomists
was that the retina, because of its abundant blood vessels, was
an organ of nutrition rather than of sight, although one Greek,
Galen, hypothesized correctly, as we now know, that the retina
was a displaced part of the brain. It was not until the 12th century
A.D, that a Moor scientist, Averroes, living in Spain, proposed
that the retina and not the lens was the visual receptor (Jung,
1984). And it was not until 500 years after Galen that Kepler
and others expanded on this principle.

Our knowledge of the eye continued to show the Arab influence
up until the 16th century (Fig. 3, left). Even the great anatomist
and artist Leonardo da Vinci (1452-1519) based his anatomical
sketches of the eye on the older incorrect Arab drawings. Leonardo
was convinced that the image was formed in the eye but did not
know how, and for the good reason that, there was still not yet
an understanding of physiological optics. In fact, it was not
until the early 17th century that more correct drawings of the
eye were made independently by the little known anatomists and
scientists, Girolamo Fabrizzi d'Aquapendente and Christopher Scheiner
(Fig. 3, right) (Polyak, 1957). By this time, the Swiss anatomist,
Platter in 1583, had proposed that the role of the lens was to
collect light rays and the retina was the photoreceptor .

Figure 3. Drawings of the structure of the eye from
the 16th and 17th century (from Polyak, 1957).

Again it was the early Greek physicists (Euclid, Archimedes
and Ptolemy) that hypothesized concerning the fundamental properties
of light: that light traveled in straight lines and could be reflected
from polished planes and curved mirrors. It seems likely that
the Greeks and then the Romans used polished glass as early magnifiers.
These items were preserved in the lava covering the destroyed
city of Pompeii (destroyed AD 79). There is little evidence for
any real design of spectacles though, until about the 13th century
A.D.. One of the earliest depictions of spectacles to correct
eyesight (Fig. 4) is shown in a man's portrait found in a church
at Rothenburgh, Germany, dating from the year 1466 (Polyak, 1957).

Johannes Kepler (1571-1630) in his Dioptrice established
the principle of dioptrics fundamental to an understanding of
how the image is formed in the eye. He understood that the cornea
and lens collected and refracted the light rays and that the image
was "painted" on the retina as an aggregation of many
image points. Kepler was also able to explain presbyopia and myopia.
Kepler was indeed the father of the science of optics (Polyak,
1957). Subsequently, many great scientists, including Rene des
Cartes (1596-1650) (Fig. 5) and Sir Isaac Newton (1642-1727)
with their work put the study of optics and ocular dioptrics on
a solid scientific foundation, from which stems all our modern
knowledge of how the eye functions and the visual image is formed.

Perceptual studies of how we see became possible as a result
of the development of mathematical formulae, and other measuring
techniques proposed in the early 17th century. They include Newton's
great discovery of the spectrum which is the foundation for the
study of color vision (Jung, 1984). The discipline, known as psychophysics
[psycho = perception and physics = physical nature of the stimulus]
is an essential discipline for probing perception. In the chapter
that follows, we outline common psychophysical procedures and
methods in use today, likely to be encountered in vision science,
optometry and ophthalmology.

2. Measurement of Light

Light can be measured and specified in two units: radiometric
units and photometric units. We consider 'light' to be a form
of visible electromagnetic radiation. It is part of the electromagnetic
spectrum between the wavelengths of 380 nm (blue light) and 750
nm (red light) (Fig. 6). Electromagnetic radiation is emitted
from a source in small packets of energy called quanta or photons.

Figure 6. Visible spectrum of the electromagnetic radiation.

In a vacuum, a photon travels at a velocity of 3 x 108
m/sec. The velocity, frequency (cycles/vibrations per second of
the photon) and the wavelength is related by this equation.

Equation 1: c = nl

where c is the velocity of light in a vacuum (e.g. m/s), n is the frequency in Hertz (e.g. cycles
per second) and l is the wavelength
(e.g. in metres). See figure 7 for this relationship. It is important
to note that the frequency is inversely proportional to the wavelength
as the velocity of light is fixed.

The velocity of light in a vacuum (c) is higher than in any
other medium (Vm). Therefore, the refractive
index in any given medium (nm), is defined as
the ratio of the two velocities. Furthermore, for any given frequency,
the wavelength in a vacuum, (lc)
and the wavelength in a medium, (lm),
gives the refractive index.

Equation 2: nm = c/Vm
= lc/lm

Energy and frequency of the photon can be related using Einstein's
equation.

Equation 3: E = hn

where E is the energy in Joules, h is Planck's
constant (6.624 x 10-34 joule·sec) and n is the frequency in Hertz (cycles per
second of the photon). The unit for energy is joules (J).

As frequency is inversely proportional to its wavelength.

Equation 4: n = c/l

where l is the wavelength in metres
and n is the frequency in Hertz (cycles
per second of the photon).

The above two equations can be combined to give.

Equation 5: E = hc/l
or Equation 6: E= hVm/lm

This fundamental equation is important in relating energy and
wavelength of light. Because energy and wavelength are inversely
proportional, this implies that short wavelength photons have
higher energy. Furthermore it is important to bear in mind that
it is only photon energy and frequency which are conserved when
light passes from one medium to another.

Another important term is power. Power is defined as the rate
of work done, that is, the amount of work or energy output over
a given time. The watt (W) is the SI unit for power. One watt
is equivalent to one joule per second.

Radiometry

There are two parallel sets of units for measuring light. One is based on the psychophysical impact of the light on a human observer, the other on detection by physical radiometric devices. The two units are interconvertible, but sometimes only with difficulty. Measurement of light energy from a source can be specified in radiometric units. Radiometric units specify the amount of radiant energy present in light. See Table 1 for radiometric concepts and SI units.

Table 1. Radiometric concepts and units.

All light measurement is derived from radiant flux. Subsequently,
radiometric units are defined with respect to direction and surface,
and all photometric units are derived from radiometric units using
the photopic luminous efficiency functions or the scotopic luminous
efficiency function.

There are two main ways in which energy produces photons, incandescent
and luminescent. These correspond to thermal and non-thermal mechanisms,
respectively. With incandescence, photons are released from thermally
agitated electrons. The frequency of photons from this type of
radiation is relatively wide and continuous regardless of the
substance, with a spectrum dependent only on temperature. Luminescence
involves electron excitation in an atom, molecule or crystal.
Emission of photons results from the energy given up by the electron
as it moves from one excitation shell to another. The frequency
of the photon emission has a pattern characteristic of the substance.

Luminescent production of photons can be achieved in a gas
discharge tube. These tubes contain gas vapour such as sodium,
mercury or neon. Electrons are accelerated from one electrode
to the other in these tubes. These high velocity electrons bombard
the gas atoms and causes a displacement of electrons. When the
electrons return to the normal state, this excitation energy is
emitted as photons. Neon and mercury sources are often used in
optics.

Fluorescence is another example of luminescence. In fluorescent
tubes, electrons collide with atoms of mercury, resulting in a
quanta of ultraviolet light being emitted. Part of the energy
of the ultraviolet quanta is absorbed by the phosphor coating
of the tube and subsequently releases a quanta of light in the
visible spectrum.

A tungsten filament lamp is an example of incandescence. Tungsten
spectral emission resembles that of a black body. A black body
is a theoretically perfect radiator. As the energy is increased,
the spectral emission changes. Colour temperature is a term used
when the colour of the radiator is the same colour as the black
body at a certain temperature (measured in Kelvin). For example,
a black body with a temperature of 2700K would have a similar
colour to tungsten, therefore, tungsten is said to have a colour
temperature of 2700K.

Photometry

Photometry is the measurement and specification of light relating
to its effect on vision. The eye can be regarded as a radiant
energy detector with a selective spectral response. In a well
lit environment it is maximally sensitive to light of about 555
nm (yellow-green light) and relatively insensitive to far red
and blue light. The function describing the response of the human
eye to different wavelengths is known as the relative luminous
efficiency function.

Measurement of light from a source can be specified in photometric
units. Photometric units take into account both the quantity of
radiant energy and sensitivity of the eye, to the wavelength(s)
of the radiation. In other words, the photometric quantities specify
the capacity of radiant energy to evoke a visual response. See
Table 2 for photometric concept and SI units.

All light measurement is derived from radiant flux, converted
to luminous flux. As with radiometric units, subsequent photometric
units are also defined with respect to direction and surface (Fig. 8).

Table 2. Photometric concepts and units.

A patient's visual fields are commonly examined in clinical
practice. The luminance of the background (bowl) of the
visual field analyser are as follows: 1) Humphrey automated visual
field analyser, 10 cd/m2. 2) Goldmann visual field
analyser, 4 cd/m2 and 3) the Medmont automated visual
field analyser, 4 cd/m2. From these values, retinal
illuminance can be calculated. Also, from table 3 (below) we can
see that the luminance of the visual field analysis places the
patient just above mesopic light levels.

V(l) versus V'(l)
is the relative luminous efficiency function used to describe
the response of the human eye to different wavelengths. The values
used are those defined by the International Commission of Illumination
(CIE) for a standard observer, as adopted in 1924 (for photopic vision) and 1951 (for scotopic vision). Thus, the photometric quantity of luminous flux is given by the equations below (Equation 7 for photopic and Equation 8 for scotopic conditions).

where Fe(l) is the corresponding radiometric quantity (in this case radiant flux) and V(l) is a luminous efficiency constant (which equals 683 lm/W for photopic conditions and 1700 lm/W for scotopic conditions), and Km is a luminous efficiency constant. Equation 8 outlines scotopic flux (Fs) in scotopic lumens from which other scotopic units, such as scotopic troland can be obtained. Convention dictates that unless otherwise stated, all units are photopic quantities.

A candela is the unit for luminous intensity. In a given direction,
it is defined as a source which emits monochromatic radiant energy
of frequency 540 x 1012 Hertz and whose radiant intensity is
1/683 watts per steradian in that direction.

A lumen (unit of luminous flux) is the luminous flux emitted
within a unit solid angle (one steradian), by a point source having
a uniform luminous intensity of one candela. Therefore, a lumen
can be defined as the luminous flux of monochromatic radiant energy
whose radiant flux is 1/683 watt and whose frequency is 540 x
1012 Hertz (converts to 555 nm in air). The definition for a
candle at 555 nm is identical for scotopic and photopic system.
Consequently, the peak of the two functions will be different,
as shown in figure 9. The amount of light required to stimulate
the eye under scotopic conditions is much less than under photopic
condition (Fig. 9). The difference in absolute sensitivity is
reflected by the different constants, Km and K'm
values for the photopic and scotopic luminous efficacy, respectively.

Figure 10 shows normalised data, where the maximum value is
set at 1 for comparison. Therefore, the curves peak at the same level.
To set the maximum at unity, the constants, Km and
K'm which correspond to the peaks of the photopic and
scotopic luminous efficacy curve respectively, are used. These
constants are used to relate back to the actual photopic luminous
efficacy, K(l), and actual scotopic
luminous efficacy, K'(l). The relationship
between K(l), V(l)
and Km are given below.

K(l) = Km V(l)
and K'(l) = K'mV'(l)

Figure 10. The scotopic and the photopic curves
of relative spectral luminous efficiency as specified by the CIE
(normalised values).

The visual system is sensitive over a wide range of luminance.
Table 3 illustrates this range. The top row shows luminances which
extend from the minimum required for detection to levels at which
damage to the visual system is possible. The second row relates
the luminance to familiar viewing conditions by indicating the
luminance of white paper under illumination from starlight to
sunlight. Finally, the bottom row links the physical stimulus
to a variety of visual functions. When patients are asked to read
the chart to measure their visual acuity as in Figure 3, their
visual system is functioning in the low photopic range.

Table 3. The dynamic range of the visual system.

SI (International Standard) units should always be used when
reporting photometric quantities (Table 4). See the Units and
Conversion Tables (Table 4) for conversion factors for some common
(and not-so-common) non-SI. To convert to SI units, multiply the
non-SI unit by the conversion factor. The best source of light measurement units is from the Light Measurements Handbook on the website http://www.intl-light.com.

Table 4: SI units and non SI units and conversion factors.

A convenient measure of retinal illuminance is based on the
unit of the troland. One troland (Td) of retinal illuminance is
produced by an extended source of 1 cd/m2 seen through
a pupil of 1 mm2. Thus retinal illuminance E in trolands
is given by Equation 9.

Equation 9: E = LA

where L is the luminance in cd/m2
and A is pupil area in mm2. Thus the unit for troland
is cd/m2.mm2. If scotopic units are used,
luminance is defined as scotopic cd/m2, and the troland
is called a scotopic troland.

Inverse Square Law

The illuminance (E) of a surface due to a point source
of light is proportional to the luminous intensity (I)
of the source in the direction of that surface and inversely proportional
to the square of the distance (d) between the surface and
the source. The angle q is the angle
of incidence.

Equation 10: E = I/d2. cos q

Remember, the rule of thumb for all laws dealing with light
measurement is that radiation is derived from a point source.
For practical purposes a source is considered to be a point source
when the distance from the source is greater that five times its
diameter.

Luminance and Illuminance calculations

When light falls on a surface, the luminance from this surface
is proportional to its reflectance and the angle of incidence.

Equation 11: L= Er/p·cos
q

where L is luminance of the
surface (cd/m2), E is the illuminance (lux), r is
the reflectance and q is the angle
of incidence of the luminous flux.

Filters

Neutral density filters are used to decrease the transmittance.
Transmittance is calculated using the following formulas.

Equation 12: T = L/Lo

Where L is luminance of the source with no filter in
place and Lo is the luminance of the source with the
filter.
The optical density of the filters is given by Equation 13.

Equation 13: D = -log10T

Where Tis the transmittance.

According to Beer's law, the optical density of a solution
is given by:

Equation 14: D = ael

Where a is the concentration of the solution in gram-molecules
per litre, e is the molar extinction coefficient and l
is the path length in cm. Equations 13 and 14 can be equated to
relate Beer's law to transmittance.

In visual field measures, the attenuation of light from the maximum available is expressed in decibel (dB) values. For example, in the Humphrey Visual Field analyser, the luminance of the light can be modulated over a 5.1 log unit range (i.e., 51dB where 0.1 log unit of attenuation = 1 dB). The maximum brightness spot is 3,183 cd/m2, and when it is attenuated with 51dB filter, it has a luminance of 0.025 cd/m2.

3. Psychophysical Measurements

Psychophysical methods and procedures are useful in determining
threshold, including visual field analysis. For a perfect observer,
threshold is the point where the stimulus can just be detected
or where you just cannot detect the stimulus. Humans are not perfect
observers, and often thresholds are defined in probabilistic terms:
for example, half the points presented would be detected and half
would not. So under certain psychophysical techniques, threshold
can be considered the point where 50% of the stimuli are detected.
Threshold variability most likely depends on neural noise. One
aspect of visual psychophysics deals with noise and is termed,
Signal Detection Theory, but this will not be covered here.

Measurement of visual response can be achieved through several
methods. These methods include the, 1) Method of Adjustment, 2)
Method of Limits, 3) Staircase (modified Method of limits) and
4) Method of Constant Stimuli.

The method of adjustment involves asking the subject
to either increase the stimulus intensity from non-seeing until
the stimulus can just be seen or to decrease the stimulus intensity
until the stimulus has just disappeared. This method also suffers
from both errors of habituation and anticipation (these two errors
are discussed below) but is useful to obtain an estimate of threshold
that can be investigated with more complex techniques. See Fig.
11.

Figure 11. Threshold determination using the method of limits. A = Ascending limits, D = Descending limits, Y = Yes, the stimulus is seen and N = No, the stimulus cannot be seen.

The method of limits involves presenting a stimulus
well above threshold and decreasing the stimulus intensity in
small steps until the subject cannot detect the stimulus (threshold).
This is called descending limits. Ascending limits is when a stimulus
is first presented well below threshold, then the stimulus intensity
is increased to reach threshold. Ascending limits and descending
limits are used to estimate the threshold. Threshold is considered
the average of the threshold points estimated by several ascending
and descending limits (Fig. 11).

Ascending and descending limits is a quick method of
determining threshold, however, like the method of adjustment,
two errors can occur; the errors of habituation and the errors
of anticipation. The error of habituation occur when subjects
develop a habit of responding to a stimulus. For example, in ascending
limits, the subject may respond to seeing the stimulus three steps
past the threshold every time, thus giving a false threshold point.
The error of anticipation occurs when subjects prematurely report
seeing the stimulus before the threshold has been reached. Clear
instructions, demonstrations and practice runs can reduce the
errors of habituation. Errors of anticipation can be minimised
by changing the starting intensity for each trial.

A variation of the method of limits is the staircase method
which involves both the ascending and descending limits in a trial.
Stimulus intensity is progressively increased (ascending limits)
until the subject reports seeing the stimulus. At this point,
the intensity value is recorded and the stimulus intensity is
then progressively reduced (descending limits), until the subject
reports not seeing the stimulus. Threshold is considered the average
of several of these reversal points. See figure 12. Threshold
estimates using this methods are also prone to the errors noted
above and consequently, multiple simultaneous staircases are used
to minimise such errors.

The method of constant stimuli involves the repeated
presentation of a number of stimuli. The threshold value of 50%
lies somewhere within this range. Other psychophysical techniques
are used to estimate threshold and determine stimuli intensities
to be used for presentation. These stimuli are randomly presented.
The percentage of detection is determined as a function of stimulus
intensity. Some high intensity points will always be detected
while other low intensity points will never to detected. The percentage
of detection versus the stimulus intensity is graphed in Figure
13. This graph is called the psychometric function and looks like
an S shaped curve sometimes referred to as an ogive. The threshold
value is defined as the value where 50% of the stimuli are detected.
Thus the threshold for the data below is 23.5.

Figure 13. Psychometric function for a YES-NO paradigm.

Psychophysical procedures are used to minimise the variability
in obtaining threshold by requiring subjects to commit to an answer.

The YES-NO PROCEDURE involves the subject judging the
presence or absence of the signal. A stimulus is presented, during
which the subject has to make a yes or no response. Correct response
can range from 0% to 100% as shown in figure 13.

The FORCED CHOICE PROCEDURE involves forcing the subject
to choose from alternative choices, one of which contains the
stimulus. A two-alternative forced choice (2AFC) describes a subject
choosing between two alternatives. Choosing from four alternatives
and six alternatives are called 4AFC and 6AFC, respectively. The
percentage correct for the various stimuli intensities can be
used to construct a psychometric function to determine threshold.
As there is already a 50% chance of a correct response with 2AFC,
threshold is commonly considered as 75% (See Fig. 14).

Figure 14. Psychometric function for 2AFC. Threshold is taken at the 75% seen level.

For a 4AFC, threshold is considered to be at the 62.5% seen
level, as this is half way between 25% and 100%. The ogive starts
at 25% because there is already a 25% chance of a correct response
with 4AFC as shown in Figure 15.

Figure 15. Psychometric function for 4AFC. Threshold is taken at the 62.5% seen level.

4. Adaptive Psychophysical
Methods

ADAPTATIVE METHODS involve presenting signals based
on the performance of the subjects previous response while in
FORCED CHOICE TRACKING a forced choice procedure is used.
When subjects correctly respond three times, stimulus intensity
is decreased by one step. An incorrect response will result in
a one step increase in stimulus intensity. The size of the ascending
and descending steps remain the same throughout the session. The
session ends when a narrow range of stimuli level is reached.
Threshold is considered the average of the intensity level within
the period of stable tracking.

The size of the steps is an important factor. If the steps
are too small, the subject may not be able to discern differences
in intensity. Reaching the threshold range with small steps will
also be time consuming. Large steps may miss the threshold range
altogether, with swings from well above threshold to well below
threshold.

PARAMETER ESTIMATION BY SEQUENTIAL TESTING (PEST) was
designed to address the problem of step size and starting intensity.
PEST techniques begin the session with large steps (large changes
in intensity) with the intensity progressively halved until the
smallest specified step to determine threshold (see Fig. 16).
PEST is actually a little more complicated than explained here.

Figure 16. Tracking record using PEST. Y = Yes, there is a stimulus and N = No, there is not a stimulus.

MAXIMUM LIKELIHOOD METHODS. With both forced choice
tracking and PEST, subsequent changes in stimulus intensity relies
on the subjects previous two or three responses. In maximum likelihood
methods, the stimulus intensity presented at each trial is determined
by statistical estimation of the subjects threshold based on all
responses from the beginning of the session. After each trial,
a new estimation of threshold is determined and the stimulus intensity
is adjusted accordingly. Threshold is taken at the point where
there is little change in stimulus intensity.

Several examples of maximum likelihood methods are QUEST (quick
estimate by sequential testing), ZEST (zippy estimate of sequential
testing), and SITA (Swedish interactive threshold algorithm -
which is a modified ZEST). These methods require prior information
about the population's distribution of threshold and is used to
construct a probability distribution function (PDF). Prior PDF
is based on previously published data, pilot studies or the expectations
of the experimenter. Based on the PDF, the mode (QUEST) or the
mean (ZEST) stimulus intensity that is most likely to be the subject's
threshold is presented. The subject's response is then used to
construct a new PDF using Bayes' rule of combining probability.
The next stimulus intensity is presented at the new level that
is most likely threshold. At the end of the procedure, the mode
(QUEST) or the mean (ZEST) of the final PDF is considered the
best estimate of the subject's threshold.

The authorMichael Kalloniatis
was born in Athens Greece in 1958. He received his optometry
degree and Master's degree from the University of Melbourne.
His PhD was awarded from the University of Houston, College of
Optometry, for studies investigating colour vision processing
in the monkey visual system. Post-doctoral training continued at the University of Texas in Houston with Dr Robert Marc. It was during this period that he developed a keen interest in retinal neurochemistry, but he also
maintains an active research laboratory in visual psychophysics
focussing on colour vision and visual adaptation. He was a faculty
member of the Department of Optometry and Vision Sciences at
the University of Melbourne for some years, moved to New
Zealandas the Robert G. Leitl Professor of Optometry,
Department of Optometry and Vision Science, University of Auckland. Since 2008 Mike has returned to Syney, Australia as a Faculty member at the University of New South Wales, and is now Director, Centre for Eye Health, an initiative of Guide Dogs NSW/ACT and the University of New South Wales (UNSW). E-mail to m.kalloniatis@unsw.edu.au

The authorCharles Luu was
born in Can Tho, Vietnam in 1974. He was educated in Melbourne
and received his optometry degree from the University of Melbourne
in 1996 and proceeded to undertake a clinical residency within
the Victorian College of Optometry. During this period, he completed
post-graduate training and was awarded the post-graduate diploma
in clinical optometry. His areas of expertise include low vision
and contact lenses. During his tenure as a staff optometrist,
he undertook teaching of optometry students as well as putting
together the "Cyclopean Eye", in collaboration with
Dr Michael Kalloniatis. The Cyclopean Eye is a Web based interactive
unit used in undergraduate teaching of vision science to optometry
students. He is currently in private optometric practice as well
as a visiting clinician within the Department of Optometry and
Vision Science, University of Melbourne.